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notes/设计模式 - 迭代器.md

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+## 迭代器（Iterator）
+
+### Intent
+
+提供一种顺序访问聚合对象元素的方法，并且不暴露聚合对象的内部表示。
+
+### Class Diagram
+
+- Aggregate 是聚合类，其中 createIterator() 方法可以产生一个 Iterator；
+- Iterator 主要定义了 hasNext() 和 next() 方法。
+- Client 组合了 Aggregate，为了迭代遍历 Aggregate，也需要组合 Iterator。
+
+<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/89292ae1-5f13-44dc-b508-3f035e80bf89.png"/> </div><br>
+
+### Implementation
+
+```java
+public interface Aggregate {
+    Iterator createIterator();
+}
+```
+
+```java
+public class ConcreteAggregate implements Aggregate {
+
+    private Integer[] items;
+
+    public ConcreteAggregate() {
+        items = new Integer[10];
+        for (int i = 0; i < items.length; i++) {
+            items[i] = i;
+        }
+    }
+
+    @Override
+    public Iterator createIterator() {
+        return new ConcreteIterator<Integer>(items);
+    }
+}
+```
+
+```java
+public interface Iterator<Item> {
+
+    Item next();
+
+    boolean hasNext();
+}
+```
+
+```java
+public class ConcreteIterator<Item> implements Iterator {
+
+    private Item[] items;
+    private int position = 0;
+
+    public ConcreteIterator(Item[] items) {
+        this.items = items;
+    }
+
+    @Override
+    public Object next() {
+        return items[position++];
+    }
+
+    @Override
+    public boolean hasNext() {
+        return position < items.length;
+    }
+}
+```
+
+```java
+public class Client {
+
+    public static void main(String[] args) {
+        Aggregate aggregate = new ConcreteAggregate();
+        Iterator<Integer> iterator = aggregate.createIterator();
+        while (iterator.hasNext()) {
+            System.out.println(iterator.next());
+        }
+    }
+}
+```
+
+### JDK
+
+- [java.util.Iterator](http://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html)
+- [java.util.Enumeration](http://docs.oracle.com/javase/8/docs/api/java/util/Enumeration.html)
+
+
+
+
+
+
+<div align="center"><img width="320px" src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/githubio/公众号二维码-2.png"></img></div>